This invention relates to a process for the preparation of isethionic acid. Isethionic acid can also be referred to as 2-hydroxyethane sulfonic acid and is of the formula HOCH.sub.2 CH.sub.2 SO.sub.3 H. Numerous processes have been suggested in the literature for the preparation of isethionic acid and the related isethionate salts.
A number of these methods are disclosed in C. M. Suter, "The Organic Chemistry of Sulfur", John Wiley & Sons, Inc. New York, 1944 (reprinted 1969), pps. 130-132. An early preparation involved the action of sulfur trioxide upon ethyl alcohol or ether to yield ethionic acid which can then be hydrolyzed to isethionic acid. The sulfonation of barium ethyl sulfate produces similar results. Another preparation involves the action of sulfur trioxide upon ethylene to form crystals of carbyl sulfate that hydrolyze first to ethionic acid and then to isethionic acid. The hydrolysis of ethionic acid to produce isethionic acid and sulfuric acid has also been described in Wooten and Lloyd, J. Org. Chem. 39, 2112 (1974) and Weinreich and Jufreso, Bull. Soc. Chem. France 1965 (3) 787; which indicate that the hydrolysis readily occurs under aqueous acid conditions. These processes all have in common the requirement of the use of sulfur trioxide, a violent reagent requiring careful and special handling techniques, and the intermediacy of carbyl sulfate or ethionic acid, which must then be hydrolyzed in aqueous solution to isethionic acid resulting in the production of sulfuric acid as a by-product. Due to the use of water as a solvent the resulting isethionic acid is obtained in a dilute solution and of concentrated is obtained as the monohydrate. Generally, these processes are not used to obtain isethionic acid per se but rather the hydrolysis mixture is neutralized with alkaline earth bases such as calcium or barium salts to precipitate the insoluble sulfate followed by the addition of alkali thereby forming the isethionate salt.
U.S. Pat. No. 4,499,028 discloses a process for the preparation of isethionic acid by treating alkali metal isethionate with hydrochloric acid in aqueous medium. This process requires excess hydrochloric acid which is not easily recovered for reuse. This process results in yields of about 80% isethionic acid containing alkali metal isethionates and water.
None of the methods of preparing isethionic acid disclosed in the prior art yield isethionic acid substantially free of contaminants such as chloride ion, sodium ion, sulfuric acid and water nor are they economical.
It is therefore an object of the present invention to provide a novel process for the preparation of isethionic acid.
It is a further object of the invention to provide a process for the preparation of isethionic acid which avoids undesirable contaminants.
It is a still further object of the invention to provide an economically desirable process for the preparation of isethionic acid.
These and other objects of the present invention will become apparent to one skilled in the art from the detailed description given hereinafter.